1. Field of the Invention
The present invention relates to a fixing device in which a high-frequency magnetic field is generated from a coil, the high-frequency magnetic field is applied to a heating member, thereby generating an eddy current in the heating member, and a developer image on a recording medium is fixed by self-generation of heat of the heating member based on an eddy-current loss.
2. Description of the Related Art
In an image forming apparatus utilizing digital technology, such as a so-called electronic copying machine, a document stage on which an original document is placed is exposed, and an image signal corresponding to the amount of light reflected from the document stage is obtained from a line sensor of CCD (charge coupled device) type. Laser beam corresponding to the image signal obtained from the line sensor is radiated on a photosensitive drum, thereby forming an electrostatic latent image on a peripheral surface of the photosensitive drum. The electrostatic latent image is developed by adhesion of a (negatively) precharged developer (toner). A paper sheet is carried to the photosensitive drum in synchronism with the rotation of the photosensitive drum. The developed image (developer image) on the photosensitive drum is transferred to the paper sheet. Then, the paper sheet on which the developer image has been transferred is fed to a fixing device.
The fixing device has a heat roller, and a press roller in contact with the heat roller. A paper sheet is inserted between the two rollers. While the paper sheet is being conveyed by the rollers, the developer image on the paper sheet is fixed by heat of the heat roller.
An induction-heating device is an example of the heat source of the heat roller. The induction-heating device comprises a coil held inside the heat roller and a high-frequency generating circuit for supplying a high-frequency current to the coil.
The high-frequency generating circuit comprises a rectifying circuit for rectifying a voltage of an AC power source and a switching circuit for converting the output voltage (DC voltage) of the rectifying circuit to a high-frequency voltage of a predetermined frequency. The aforementioned coil is connected to an output terminal of the high-frequency generating circuit (an output terminal of the switching circuit).
When the high-frequency generating circuit operates, a high-frequency current is supplied to the coil, with the result that a high-frequency magnetic field is generated from the coil. The high-frequency magnetic field is applied to the heat roller, and an eddy current is generated in the heat roller. Then, the heat roller is self-heated owing to an eddy current loss. The developer image on the paper sheet is fixed by the heat.
An electric wire (a so-called lead) lies between the high-frequency generating circuit and the coil. The high-frequency magnetic field generated from the electric wire may influence another part existing around the electric wire, resulting in a possibility of unnecessary heat generation of the part.
The present invention was made in consideration of the above situations. An object of the present invention is to overcome the drawback that the high-frequency magnetic field may adversely influence another part.
A fixing device according to the present invention having a coil in a heat roller, causing the coil to generate a high-frequency magnetic field, thereby generating an eddy current in the heat roller, and fixing a developer image on a recording medium by self-generation of heat of the heat roller based on an eddy-current loss, the fixing device comprising:
a high-frequency generating circuit for outputting a high-frequency current to generate a high-frequency magnetic field from the coil;
an electric wire for supplying the output of the high-frequency generating circuit to the coil; and
a shield member for magnetically shielding the electric wire.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.